Electronic device with adjustable reverse breakdown voltage

ABSTRACT

An electrical device may include a substrate; a first doped region of the substrate having a p doping type; a second doped region adjacent to the first doped region of the substrate having an n doping type, wherein an interface between the first and second doped regions forms a p-n junction; and a circuit element placed in spaced relation to the p-n junction, the circuit element configured to produce an electric field that interacts with the p-n junction to change a reverse breakdown voltage of the p-n junction. Applicants for the electrical device include ESD protection circuits.

FIELD

This disclosure relates to electronic device with breakdown voltagesand, in particular, to electronic device with adjustable breakdownvoltages.

BACKGROUND

Diodes allow current to flow in one direction. However, if a high enoughreverse voltage is applied to a diode, the diode will allow current toflow in the opposite direction through the diode. The voltage requiredto drive current though the diode in the reverse direction is referredto as the reverse breakdown voltage, or simply the breakdown voltage.Some diodes, such as Zener diodes, have relatively low breakdownvoltages that are utilized in various circuit designs. For example,electrostatic discharge (ESD) protection circuits may utilize Zenerdiodes to block current from flowing under normal voltage conditions,and to allow current to flow through the diode in the reverse directionunder high voltage conditions.

SUMMARY

In an embodiment, an apparatus includes: a substrate; a first dopedregion of the substrate having a p doping type; a second doped regionadjacent to the first doped region of the substrate having an n dopingtype, wherein an interface between the first and second doped regionsforms a p-n junction; and a circuit element placed in spaced relation tothe p-n junction, the circuit element configured to produce an electricfield that interacts with the p-n junction to change a reverse breakdownvoltage of the p-n junction.

In another embodiment, an apparatus includes a substrate; a Zener diodeformed in the substrate with an adjustable reverse breakdown voltage,the Zener diode comprising: a first doped region of the substrate havinga first doping type; a second doped region having a second doping typepositioned adjacent to the first doped region of the substrate, whereinan interface between the first and second doped regions forms a p-njunction; a field plate placed in spaced relation to the p-n junction,the field plate configured to produce an electric field that interactswith the p-n junction to change a reverse breakdown voltage of the p-njunction; and a biasing circuit to generate a voltage on the field plateto generate the electric field.

In another embodiment, an ESD protection circuit includes: a firstterminal; a second terminal; an adjustable Zener diode coupled in seriesbetween the first and second terminals, the adjustable Zener diodehaving an anode, a cathode, and a control input node, wherein a voltageapplied to the control input node alters a reverse breakdown voltage ofthe Zener diode.

In another embodiment, an ESD protection circuit includes: an ESD clampcircuit comprising an npn transistor; and an adjustable Zener diodehaving an adjustable reverse breakdown voltage and a control input nodeconfigured to receive a voltage that adjusts the reverse breakdownvoltage; wherein control of the input node of the adjustable Zener diodeis coupled to one of the two collectors of the npn transistor. Thenpn-transistor may be a two-collector npn transistor.

In another embodiment, an integrated circuit includes a substrate; and atest circuit comprising: a Zener diode formed in the substrate with anadjustable reverse breakdown voltage. The Zener diode includes a firstdoped region of the substrate having a p doping type; a second dopedregion having an n doping type positioned adjacent to the first dopedregion of the substrate, wherein an interface between the first andsecond doped regions forms a p-n junction; a field plate placed inspaced relation to the p-n junction, the field plate configured toproduce an electric field that interacts with the p-n junction to changea reverse breakdown voltage of the p-n junction; and a biasing circuitto generate a voltage on the field plate to generate the electric field;wherein the Zener diode is coupled in parallel with a protected circuitand configured to protect the protected circuit from overstressconditions; and wherein the biasing circuit is configured to generate afirst voltage during normal operation of the integrated circuit and asecond voltage during testing of the integrated circuit.

In another embodiment, an apparatus includes a first terminal; a secondterminal; one or more conduction path circuits coupled between the firstand second terminals, each conduction path circuit comprising a Zenerdiode with an adjustable reverse breakdown voltage, each Zener diodecomprising a control input node to receive an analog voltage thatcontrols the adjustable reverse breakdown voltage; wherein theconduction path circuit includes an input terminal to receive an enablesignal which, when activated, allows the conduction path circuit toconduct electrical current between the first and second terminals; and acontrol circuit coupled to the control input nodes of the Zener diodesof the one or more conduction path circuits, the control circuitconfigured to generate the analog voltage and selectively control theadjustable reverse breakdown voltage of the Zener diodes to controlcurrent flow through the one or more conduction path circuits.

In another embodiment, an apparatus comprises: a substrate; a firstdoped region of the semiconductor substrate having a p doping type; asecond doped region adjacent to the first doped region of thesemiconductor substrate having an n doping type, wherein an interfacebetween the first and second doped regions forms a p-n junction; andmeans for producing an electric field that interacts with the p-njunction to change a reverse breakdown voltage of the p-n junction.

In another embodiment, an ESD protection circuit comprises: a firstterminal; a second terminal; a Zener diode coupled in series between thefirst and second terminals, the Zener diode comprising means foradjusting a breakdown voltage of the Zener diode; and circuit means foradjusting the breakdown voltage during operation of the ESD protectioncircuit.

Additional embodiments may fall within the scope of this disclosure andthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features may be more fully understood from the followingdescription of the drawings. The drawings aid in explaining andunderstanding the disclosed technology. Since it is often impractical orimpossible to illustrate and describe every possible embodiment, theprovided figures depict one or more exemplary embodiments. Accordingly,the figures are not intended to limit the scope of the invention. Likereference numbers in the figures denote like elements.

FIG. 1 is a cross-sectional view of an integrated circuit supporting anelectronic device with an adjustable reverse breakdown voltage.

FIG. 2A is a cross-sectional view of another embodiment of an integratedcircuit supporting an electronic device with an adjustable reversebreakdown voltage.

FIG. 2B is a graph of a current-voltage (“IV”) curve of an electronicdevice with an adjustable reverse breakdown voltage.

FIG. 3A is a cross-sectional view of another embodiment of an integratedcircuit supporting an electronic device with an adjustable reversebreakdown voltage.

FIG. 3B is a graph of a current-voltage (“IV”) curve of an electronicdevice with an adjustable reverse breakdown voltage.

FIG. 4 is a cross-sectional view of another embodiment of an integratedcircuit supporting an electronic device with an adjustable reversebreakdown voltage.

FIG. 5 is a cross-sectional view of another embodiment of an integratedcircuit supporting an electronic device with an adjustable reversebreakdown voltage.

FIG. 6 is a cross-sectional view of another embodiment of an integratedcircuit supporting an electronic device with an adjustable reversebreakdown voltage.

FIG. 7 is a circuit diagram of a circuit utilizing a Zener diode with anadjustable reverse breakdown voltage.

FIG. 8 is a circuit diagram of a circuit utilizing a Zener diode with anadjustable reverse breakdown voltage and corresponding IV curve.

FIG. 9 is a circuit diagram of an electrostatic discharge (“ESD”)protection circuit utilizing a Zener diode with an adjustable reversebreakdown voltage.

FIG. 10 is a circuit diagram of another embodiment of an ESD protectioncircuit utilizing a Zener diode with an adjustable reverse breakdownvoltage and corresponding IV curve.

FIG. 11 is a circuit diagram of another embodiment of an ESD protectioncircuit utilizing a Zener diode with an adjustable reverse breakdownvoltage and corresponding IV curve.

FIG. 12 is a circuit diagram of a circuit having multiple ESD protectioncircuits utilizing a Zener diodes with adjustable reverse breakdownvoltages.

DETAILED DESCRIPTION

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can be, but is not limited to,a Hall Effect element, a magnetoresistance element, or amagnetotransistor. As is known, there are different types of Hall Effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, an anisotropicmagnetoresistance element (AMR), a tunneling magnetoresistance (TMR)element, and a magnetic tunnel junction (MTJ). The magnetic fieldsensing element may be a single element or, alternatively, may includetwo or more magnetic field sensing elements arranged in variousconfigurations, e.g., a half bridge or full (Wheatstone) bridge.Depending on the device type and other application requirements, themagnetic field sensing element may be a device made of a type IVsemiconductor material such as Silicon (Si) or Germanium (Ge), or a typeIII-V semiconductor material like Gallium-Arsenide (GaAs) or an Indiumcompound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elementstend to have an axis of maximum sensitivity parallel to a substrate thatsupports the magnetic field sensing element, and others of theabove-described magnetic field sensing elements tend to have an axis ofmaximum sensitivity perpendicular to a substrate that supports themagnetic field sensing element. In particular, planar Hall elements tendto have axes of sensitivity perpendicular to a substrate, while metalbased or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) andvertical Hall elements tend to have axes of sensitivity parallel to asubstrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back-biased or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

FIG. 1 is a cross sectional diagram of an integrated circuit supportingan electronic device 100 with adjustable turn-on voltage. In anembodiment, electronic device 100 may be a Zener, avalanche, or othertype of diode. For ease of explanation, this disclosure discusses Zenerdiode. However, one skilled in the art will recognize that other typesof diodes or devices may be used in place of Zener diodes asappropriate.

Electronic device 100 may include a substrate 102, which may comprise amaterial that can support integrated circuits. In embodiments, thesubstrate may comprise a semiconductor material such as silicon,germanium, gallium arsenide, or any other type of semiconductormaterial. In other embodiments, substrate 102 may comprise a glass orceramic material that can support integrated circuits.

Substrate 102 may include a p-doped well (“p-well”) 104. An n-dopedregion 106 may be formed within p-well 104. Additionally, a p-dopedregion 108 may also be formed within p-well 104. P-doped region 108 mayprovide a low resistive contact to terminal 110. In embodiments, p-dopedregion 108 may be more strongly doped than p-well 104.

For ease of illustration, well 104 is described as p-doped, region 106is described as n-doped, and region 108 is described as p-doped.However, one skilled in the art will recognize that the doping of theseregions can be reversed to obtain similar or opposite characteristics ofelectronic device 100. For example, if the doping polarity is reversed,the resulting device may be a Zener diode with a negative breakdownvoltage that breaks down when an applied voltage is less than thenegative breakdown voltage.

Electronic device 100 may include field plate 112 placed adjacent to PNjunction 114 between n-doped region 106 and p-well 104. A dielectriclayer 116 may be positioned between field plate 112 and substrate 102 togalvanically isolate field plate 112 from substrate 102 and the dopedregions.

PN junction 114 may act as a diode where terminal 110 (coupled top-doped region 108) is the anode and terminal 118 (coupled ton-doped-region 106) is the cathode. When the diode is forward biased,current may flow from anode terminal 110, into p-doped region 108, intop-well 104, into n-doped region 106, and finally to cathode terminal118.

In an embodiment, electronic device 100 may be constructed as a Zenerdiode. Accordingly, when the Zener diode is reverse biased with avoltage that exceeds the Zener diode's breakdown voltage, current mayflow from cathode terminal 118 to n-doped region 106, to p-well 104, top-doped region 108, and finally to anode terminal 110.

If a voltage is applied to field plate 112, it may create anelectrostatic field that can change the reverse breakdown voltage of PNjunction 114. For example, the electrostatic field may modulate thesurface concentration of free carriers in the region of the PN junctionthat the field plate overlaps. A positive bias voltage applied to fieldplate 112 (with respect to anode terminal 110) may repel holes from thesurface of p-well region 104, pushing them deeper into the bulk ofp-well region 104 towards substrate 102. This may effectively lower thedoping concentration of p-well 104 near PN junction 114, and thusincrease the breakdown voltage of PN junction 114. Conversely, anegative bias voltage (with respect to anode terminal 110) may attractadditional holes, effectively increasing the doping concentration ofp-well 104 near PN junction 114. This may cause a decrease in thebreakdown voltage of PN junction 114.

Referring to FIG. 2A, electronic device 100′ may be the same as orsimilar to electronic device 100 of FIG. 1. In FIG. 2A, field plate 112may be coupled to anode terminal 110. In a situation where electronicdevice 100′ is reverse biased, this coupling may effectively lower thebias voltage of field plate 112 with respect to the voltage on anodeterminal 110, and thus decrease the reverse breakdown voltage of PNjunction 114, as described above.

FIG. 2B is an IV curve that illustrates the change in the reversebreakdown voltage. The horizontal axis represents the voltage from anodeterminal 110 to cathode terminal 118, and the vertical axis representsthe current through electronic device 110′. If field plate 112 remainsunbiased (as shown in FIG. 1), the reverse breakdown voltage may be V1.If the voltage on field plate 112 is reduced (for example by couplingfield plate 112 to anode terminal 110 as shown in FIG. 2A), then thereverse breakdown voltage may decrease to V1′.

Referring to FIG. 3A, electronic device 100″ may be the same as orsimilar to electronic device 100 of FIG. 1. In FIG. 3A, field plate 112may be coupled to cathode terminal 118. In a situation where electronicdevice 100″ is reverse biased, this coupling may effectively raise thebias voltage of field plate 112 with respect to the voltage on anodeterminal 110, and thus increase the reverse breakdown voltage of PNjunction 114, as described above.

FIG. 3B is an IV curve that illustrates the change in the reversebreakdown voltage. The horizontal axis represents the voltage from anodeterminal 110 to cathode terminal 118, and the vertical axis representsthe current through electronic device 110″. If field plate 112 remainsunbiased (as shown in FIG. 1), the reverse breakdown voltage may be V2.If the voltage on field plate 112 is increased with respect to thevoltage on anode terminal 110 (for example by coupling field plate 112to anode cathode terminal 118 as shown in FIG. 3A), then the reversebreakdown voltage may increase to V2′.

Referring now to FIG. 4, electronic device 400 includes field plate 112,which may be coupled to terminal 402. In embodiments, terminal 402 maybe coupled to external circuitry that controls a voltage applied tofield plate 112, and thus can control the value of the reverse breakdownvoltage of PN junction 114.

Referring to FIG. 5, electronic device 500 may be the same as or similarto electronic device 400. Electronic device 500 may include additionalcircuitry to control the bias voltage applied to field plate 112, andthus control the reverse breakdown voltage of PN junction 114. As shownin FIG. 5, the additional circuitry may be as resistor divider circuitcomprising resistor R1 and resistor R2. Resistors R1 and R2 may bechosen to bias the voltage on field plate 112 toward the voltage onanode terminal 110 or toward the voltage on cathode terminal 118. Asnoted above, biasing the voltage on field plate 112 toward the voltageon anode terminal 110 may reduce the value of the breakdown voltage ofPN junction 114, and biasing the voltage on field plate 112 toward thevoltage on cathode terminal 118 may increase the value of the breakdownvoltage of PN junction 114.

Referring to FIG. 6, electronic device 600 may be the same as or similarto electronic device 400. Electronic device 600 may include a circuit(shown by circuit elements 602 and 604) to control the voltage appliedto field plate 112. In embodiments, circuits 602 and 604 may includereactive elements like capacitors or inductors, and/or active elementslike transistors or diodes, or more complex circuits. Circuits 602 and604 may implement a function that controls the voltage on field plate112. The function may be a function of frequency, current, voltage,etc., and may dynamically alter the breakdown voltage of PN junction 114while under operation.

Referring to FIG. 7, circuit 700 may utilize a Zener diode 702 with anadjustable reverse breakdown voltage. Zener diode 702 may be the same asor similar to electronic device 400 described above. As shown, Zenerdiode 702 may include cathode terminal 118, anode terminal 110, andfield plate terminal 402.

In embodiments, terminal 402 may be coupled to an external circuit 704that controls the voltage at terminal 402, and thus controls the valueof the reverse breakdown voltage of Zener diode 702. In embodiments,signal 704 a produced by external circuit 704 may be an analog signal.As shown in FIG. 7, signal 704 a may be produced by a digital-to-analogconverter (“DAC”) 706, powered by voltage regulator 708. Of course,other circuits may be coupled to terminal 402. Circuit 700 is simply anexample of a circuit for controlling the reverse breakdown voltage ofZener diode 702. Other applications include a reference Zener diode fora voltage regulator, adjustable programmable references, adjustablebreakdown voltage blocking diode for IC testing, etc.

Referring to FIG. 8, circuit 800 is an electrical overstress protectioncircuit that includes a Zener diode 802 with an adjustable reversebreakdown voltage. Zener diode 802 may be the same as or similar toelectronic device 400, and may include anode terminal 110, cathodeterminal 118, and field plate terminal 402.

Zener diode 802 may act as a protection circuit to reduce the chancethat protected circuit 804 becomes damaged by an electrical overstresscondition, such as an electro-static discharge (“ESD”) event, anovercurrent event, or the like. In the case of electrical overstressevent, current may flow through Zener diode 802 rather than throughprotected circuit 804.

Circuit 800 may also include a control circuit 806 coupled to DAC 808.The output of DAC 808 may be coupled to field plate terminal 402 tocontrol the reverse breakdown voltage of Zener diode 802. The output ofcontrol circuit 806 may, for example, cause DAC 808 to provide a desiredvoltage to terminal 402 to control the reverse breakdown voltage ofZener diode 802. Control circuit 806 may include various circuits and/orcircuit elements that can implement a function to control the reversebreakdown voltage.

In one example, Zener diode 802 may be used for testing an integratedcircuit. In an embodiment, circuit 800 may be an integrated circuitsupported by a semiconductor substrate and enclosed in a chip package.During normal operation, control circuit 806 may provide a nominalvoltage to terminal 402 so that Zener diode 802 acts as an electricaloverstress protection circuit. In embodiments, the nominal voltage mayprovide a reverse breakdown voltage of 8V, as shown by line 810 in IVcurve 812.

In embodiments, when the circuit is placed in test mode, control circuit806 may increase the voltage applied to terminal 402, thus increasingthe value reverse breakdown voltage to 12V, as shown by line 814 in IVcurve 812. Increasing the value of the reverse breakdown voltage fortests such as a short overvoltage (“SHOVE”) test (e.g. a test toidentify potentially weak CMOS gates in an integrated circuit), aburn-in test, or a Load Dump test, for example, may avoid falseactivation of the electrical overstress protection circuit, and falsefailures of the test. In embodiments, Zener diode 802 may be replaced byan electrical overstress protection circuit, such as an ESD clampcircuit, that utilizes a Zener diode with an adjustable reversebreakdown voltage.

In some applications, design specifications may require the VCC pin ofan automotive circuit to withstand 10 kV of electrostatic discharge andtrigger an overvoltage condition at approximately 42 Volts underoperation. In such a circuit, Zener diode 802 may be designed to have abreakdown voltage of 42 Volts during normal operation. However, it maybe desirable to reduce the breakdown voltage of Zener diode 802 to 30Volts, for example, in the case of an ESD event. If an ESD event isdetected, control circuit 806 may reduce the breakdown voltage of Zenerdiode 802 (or an ESD clamp circuit that utilizes Zener diode 802) to 30Volts. The ESD event may be detected by any number of ways known in theart including, but not limited to, a comparator that compares voltageacross the terminals to a predetermined threshold, a shunt resistor orcurrent meter to measure current through the Zener diode, etc.

Reducing the breakdown voltage of Zener diode 802 may allow current topass through Zener diode 802 during an ESD event, but also block currentfrom flowing through Zener diode 802 during an overvoltage condition upto 42 Volts during normal operation when the VCC voltage is below theovervoltage threshold of 42 volts.

Referring to FIG. 9, circuit 900 may be an ESD clamp circuit thatutilizes a Zener diode 902 with an adjustable reverse breakdown voltage.Zener diode 902 may be the same as or similar to electronic device 400,having cathode terminal 118, anode terminal 110, and field plateterminal 402.

ESD clamp circuit 900 may include NPN BJT transistors Q1 and Q2 arrangedin a Darlington array formation to produce a so-called Darlington ESDclamp circuit. If the voltage at terminal 904 exceeds the reversebreakdown voltage of Zener diode 902, current will flow through Zenerdiode 902 into the base of transistor Q1. Subsequently, transistor Q1will drive current into the base of transistor Q2 turning transistor Q2on, allowing current to flow from terminal 904, through Q2, to ground.

Field plate terminal 402 may be coupled to collector terminal 906 oftransistor Q2. As current begins to flow through transistor Q2 andresistor 908, the voltage at field plate terminal 402 will change, thuschanging the reverse breakdown voltage of Zener diode 902 duringoperation of ESD clamp circuit 900. In embodiments, this may result inan ESD clamp with a so-called S characteristic of its IV curve.

Turning to FIG. 10, circuit 1000 is another embodiment of an ESD clampcircuit utilizing a Zener diode 1002 with an adjustable reversebreakdown voltage. Zener diode 1002 may be the same as or similar toelectronic device 400, having cathode terminal 118, anode terminal 110,and field plate terminal 402.

Field plate terminal 402 may be coupled to collector terminal 1006 oftransistor Q2. Similar to circuit 900, as current begins to flow throughtransistor Q2 and resistor 1008, the voltage at field plate terminal 402will change, thus changing the reverse breakdown voltage of Zener diode1002 during operation of ESD clamp circuit 1000.

Graph 1010 is an IV curve that illustrates the S characteristic of ESDclamp circuit 1000. The S characteristic is so named based on the S-likeshape of the IV curve over time. Points 1 through 4 on IV curve 1010represent the progression of the IV characteristic over time during anelectrical overstress event.

When ESD clamp 1000 is in a stable state, with no current flowing, thebreakdown voltage of Zener diode 1002 may be about 14 Volts. As thevoltage between terminals 1012 and 1014 increases to the Zener diode'sbreakdown voltage (shown by point 2 in graph 1010), current may start toflow through Zener diode 1002 and place transistors Q1 and Q2 inconducting states. As current begins to flow through resistor 1008, thevoltage at field plate terminal 402 may decrease with respect to thevoltage at cathode terminal 118, thus reducing the value of thebreakdown voltage of Zener diode 1002, as shown by point 3 in graph1010. As current continues to increase through Q2, the breakdown voltagemay increase linearly as shown by the curve between points 3 and 4.

Turning to FIG. 11, circuit 1100 is another embodiment of an ESD clampcircuit utilizing a Zener diode 1102 with an adjustable reversebreakdown voltage. Zener diode 1102 may be the same as or similar toelectronic device 400, having cathode terminal 118, anode terminal 110,and field plate terminal 402. However, Zener diode 1102 may have reversedoping polarity with respect to electronic device 400. For example, thep-doped areas in electronic device 400 may be replaced by n-doped areasin Zener diode 1102, and the n-doped areas in electronic device 400 maybe replaced by p-doped areas in Zener diode 1102.

In circuit 1100, field plate terminal 402 may be coupled to emitterterminal 1106 of transistor Q2. Similar to circuits 900 and 1000, ascurrent begins to flow through transistor Q2 and resistor 1108, thevoltage at field plate terminal 402 will change, thus changing thereverse breakdown voltage of Zener diode 1102 during operation of ESDclamp circuit 1100.

Graph 1110 is an IV curve that illustrates the S characteristic of ESDclamp circuit 1100. Points 1 through 4 on IV curve 1110 represent theprogression of the IV characteristic over time during an electricaloverstress event.

When ESD clamp 1100 is in a stable state, with no current flowing, thebreakdown voltage of Zener diode 1102 may be about 14 Volts. As thevoltage between terminals 1112 and 1114 increases to the Zener diode'sbreakdown voltage (shown by point 2 in graph 1110), current may start toflow through Zener diode 1102 and place transistors Q1 and Q2 inconducting states. As current begins to flow through resistor 1108, thevoltage at field plate terminal 402 may decrease with respect to thevoltage at cathode terminal 118, thus reducing the value of thebreakdown voltage of Zener diode 1102, as shown by point 3 in graph1110. As current continues to increase through Q2, the breakdown voltagemay increase linearly as shown by the curve between points 3 and 4.

Referring to FIG. 12, circuit 1200 may be an electrical overstressprotection circuit having a plurality of ESD clamp circuits 1202-1208and a clamp control circuit 1210. ESD clamp circuit 1202-1208 may besimilar to ESD clamp circuits 900, 1000, 1100, and/or 1200 describedabove. For example, each ESD clamp circuit 1202-1208 may be anadjustable Zener diode protection circuit, a Darlington arrayincorporating an adjustable Zener diode, or any other type of ESD clampcircuit that may utilize an adjustable Zener diode.

In particular, each clamp circuit 1202-1208 may incorporate a Zenerdiode with an adjustable reverse breakdown voltage. However, the fieldplate terminal (i.e. the terminal that controls the reverse breakdownvoltage) of each ESD circuit 1202-1208 may be coupled to clamp controlcircuit 1210, as shown by bus line 1212. Accordingly, clamp controlcircuit 1210 may control the reverse breakdown voltage (and thus thevoltage at which each clamp circuit will conduct current) for each ofthe ESD clamp circuits 1202-1208.

Clamp control circuit 1210 may be configured to selectively adjust thereverse breakdown voltage of ESD clamp circuits 1202-1208. Clamp controlcircuit 1210 may include a level detect circuit 1214 that senses anovervoltage condition. For example, level detect circuit 1214 may sensethe voltage between terminal 1216 and terminal 1218 to determine if itexceeds a predetermined threshold indicating an overvoltage condition.Level detect circuit 1214 may include a comparator or other circuitry todetect whether the voltage (or current) between terminals 1216 and 1218exceeds a particular threshold voltage (or current). Clamp controlcircuit 1210 may also include a low pass filter 1220 coupled to leveldetect circuit 1214. Low pass filter 1220 may block high-frequency noiseon the voltage signal at terminal 1216 in order to reduce the chancethat noise on the voltage signal will cause clamp control circuit 1220to erroneously detect an overvoltage condition.

Clamp control circuit 1210 may also include a clock circuit 1222 andcontrol signal generator circuit 1226. Clock circuit 1222 may provide aclock signal 1224 to control signal generator circuit 1226. When controlsignal generator circuit 1226 receives clock signal 1224, control signalgenerator circuit 1226 may drive individual signal lines of bus 1212high and low to selectively adjust the breakdown voltages of ESD clampcircuits 1202-1208. In the embodiment shown, clamp circuit 1210 maycontrol the breakdown voltages of ESD clamp circuits 1202-1208 byturning clock circuit 1222 on or off. When clock circuit 1222 is on,control signal generator circuit 1226 drives bus 1212 with analogsignals to control the breakdown voltages of ESD clamp circuits1202-1208. When clock circuit 1222 is off, control signal generatorcircuit 1226 may not drive bus 1212.

In other embodiments, clock 1222 and control signal generator circuit1226 may be replaced by any circuit or processor that can drive bus 1212with analog, digital, or switched signals to control the breakdownvoltages of ESD clamp circuits 1202-1208. Such circuits may include aprocessor executing software or firmware, a shift register, a patterngenerator, analog-to-digital converter, etc.

Circuit 1200 may also include a temperature sensing circuit 1228configured to measure the temperature of ESD protection circuit1202-1208. Temperature sensing circuit 1228 may be coupled totemperature sensors 1230-1236, which may be positioned near a respectiveESD protection circuit 1202-1208. In an embodiment, temperature sensors1230-1236 are diodes having temperature dependencies. Temperaturesensing circuit 1228 may measure the current through the respectivediodes to determine the temperature at or near a respective ESDprotection circuits 1202-1208.

In operation, level detect circuit 1214 may detect whether an electricaloverstress condition is present between terminals 1216 and 1218 by, forexample, comparing the voltage between those terminals to apredetermined threshold voltage. If an overvoltage condition exists,level detect circuit 1214 may activate clock 1222 which, in turn, mayactivate control signal generator circuit 1226. Control signal generatorcircuit 1226 may selectively adjust the breakdown voltage of ESDprotection circuit 1202-1208 so that one or more of ESD protectioncircuits 1202-1208 will conduct current between terminals 1216 and 1218in response to the detected overvoltage condition. Control signalgenerator circuit 1226 may also selectively adjust the breakdown voltageof ESD protection circuit 1202-1208 to control the amount of currentflowing through each ESD protection circuit 1202-1208.

In an embodiment, temperature sensing circuit 1228 may measure thetemperature of each ESD protection circuit 1202-1208 (by, for example,measuring the current through temperature sensing diodes 1230-1236) andtransmit the measured temperature to clamp control circuit 1210. If themeasured temperature of any of the ESD protection circuit 1202-1208 istoo high (e.g. if the measured temperature exceeds a predeterminedthreshold or tolerance), clamp control circuit 1210 may adjust thebreakdown voltage of that particular ESD protection circuit to turn theESD protection circuit off or limit the amount of current flowingthrough the ESD protection circuit.

Various clamp control circuits may be used in place of clamp controlcircuit 1210 to adjust the breakdown voltages of ESD protection circuit1202-1208 in response to various conditions. Examples may be found inU.S. patent application Ser. No. 15/272,784 (filed Sep. 22, 2016). Someof the clamp control circuits in U.S. patent application Ser. No.15/272,784 may be configured to turn ESD protection circuits on and off.However, they may be modified to similarly adjust a breakdown voltage ofan ESD protection circuit like circuit 1200 above.

Having described preferred embodiments, which serve to illustratevarious concepts, structures and techniques, which are the subject ofthis patent, it will now become apparent to those of ordinary skill inthe art that other embodiments incorporating these concepts, structuresand techniques may be used. Accordingly, it is submitted that that scopeof the patent should not be limited to the described embodiments butrather should be limited only by the spirit and scope of the followingclaims. All references cited in this disclosure are incorporated here byreference in their entirety.

The invention claimed is:
 1. An apparatus comprising: a substrate; afirst doped region of the semiconductor substrate having a p dopingtype; a second doped region adjacent to the first doped region of thesemiconductor substrate having an n doping type, wherein an interfacebetween the first and second doped regions forms a p-n junction; acircuit element placed in spaced relation to the p-n junction, thecircuit element configured to produce an electric field that interactswith the p-n junction to change a reverse breakdown voltage of the p-njunction, wherein the circuit element comprises a field plate positionedin spaced relationship to the p-n junction to produce the electricfield; and; a biasing circuit that produces a voltage on the fieldplate, which produces the electric field that interacts with the p-njunction to change the reverse breakdown voltage of the p-n junction,wherein the biasing circuit is configured to produce an adjustablevoltage on the field plate, wherein adjusting the voltage consequentlychanges the value of the reverse breakdown voltage.
 2. The apparatus ofclaim 1 wherein the first doped region and the second doped region forma Zener diode or an avalanche diode.
 3. The apparatus of claim 2 whereinthe circuit element generates an electric field that changes a value ofthe reverse breakdown voltage.
 4. The apparatus of claim 1 wherein thebiasing circuit comprises one or more of: an active circuit element anda passive circuit element.
 5. The apparatus of claim 1 wherein thebiasing circuit is configured to adjust the adjustable voltage inresponse to a received stimulus.
 6. The apparatus of claim 5 furthercomprising an ESD detection circuit coupled to the biasing circuit,wherein the received stimulus is a signal produced by the ESD detectioncircuit in response to detection of an ESD event.
 7. An apparatuscomprising: a substrate; a Zener diode formed in the substrate with anadjustable reverse breakdown voltage, the Zener diode comprising: afirst doped region of the substrate having a first doping type; a seconddoped region having a second doping type positioned adjacent to thefirst doped region of the substrate, wherein an interface between thefirst and second doped regions forms a p-n junction; and a field plateplaced in spaced relation to the p-n junction, the field plateconfigured to produce an electric field that interacts with the p-njunction to change a reverse breakdown voltage of the p-n junction; anda biasing circuit to generate a voltage on the field plate to generatethe electric field; wherein the biasing circuit is configured togenerate an adjustable voltage.
 8. An ESD protection circuit comprising:a first terminal; a second terminal; an adjustable Zener diode coupledin series between the first and second terminals, the adjustable Zenerdiode having an anode, a cathode, and a control input node, wherein avoltage applied to the control input node alters a reverse breakdownvoltage of the Zener diode; and an ESD detection circuit coupled to thecontrol input node and configured to generate the voltage applied to thecontrol input node in response to detection of an ESD event, wherein theESD detection circuit comprises one or more switches to selectivelycouple and/or decouple the control input node from a ground node.
 9. TheESD protection circuit of claim 8 wherein the ESD protection circuitcomprises a substrate and the adjustable Zener diode comprises: a firstdoped region of the substrate having a p doping type; a second dopedregion having an n doping type positioned adjacent to the first dopedregion of the substrate, wherein an interface between the first andsecond doped regions forms a p-n junction; and a field plate placed inspaced relation to the p-n junction, the field plate configured toproduce an electric field that interacts with the p-n junction to changea reverse breakdown voltage of the p-n junction; wherein the field plateis coupled to the control input node to receive the voltage applied tothe control input node.
 10. An apparatus comprising: a first terminal; asecond terminal; one or more conduction path circuits coupled betweenthe first and second terminals, each conduction path circuit comprisinga Zener diode with an adjustable reverse breakdown voltage, each Zenerdiode comprising a control input node to receive an analog voltage thatcontrols the adjustable reverse breakdown voltage; wherein theconduction path circuit includes an input terminal to receive an enablesignal which, when activated, allows the conduction path circuit toconduct electrical current between the first and second terminals; and acontrol circuit coupled to the control input nodes of the Zener diodesof the one or more conduction path circuits, the control circuitconfigured to generate the analog voltage and selectively control theadjustable reverse breakdown voltage of the Zener diodes to controlcurrent flow through the one or more conduction path circuits.
 11. Theapparatus of claim 10 wherein the control circuit further comprises oneor more digital-to-analog converters to produce the analog voltage. 12.The apparatus of claim 10 further comprising one or more temperaturesensors to detect a temperature of a respective conduction path circuitand provide a temperature signal to the control circuit.
 13. Theapparatus of claim 12 wherein the control circuit selectively controlsthe adjustable reverse breakdown voltage of the Zener diodes in responseto the temperature signals.
 14. The apparatus of claim 10 wherein eachZener diode further comprises: a first doped region of a substratehaving a p doping type; a second doped region having an n doping typepositioned adjacent to the first doped region of the substrate, whereinan interface between the first and second doped regions forms a p-njunction; and a field plate placed in spaced relation to the p-njunction, the field plate configured to produce an electric field thatinteracts with the p-n junction to change a reverse breakdown voltage ofthe p-n junction; wherein the field plate is coupled to the controlinput node to receive the analog voltage.